SO been there done that!
A few short months ago, I traveled cross country (from VA to WA) with
many cats.
We had two running free (their ages 2 and 3) in my Nissan Armada, and one cat was in an XL
dog kennel cage in the back. Then I drove (my son drove the Armada) my husband's Mercury Grand Marquis with two additional cats. We had one litter box in each (+the one in the kennel), one food bowl, and one water bowl. Then each
cat had a kitty bed or cozy cube. One of my cats liked going back into the open cat kennel we left on one of the seats.
The ones in the Mercury are ages 11 and 5/6 (shelter kitty, not positive). We had another 2 in a uhaul cab out in the open as well. They mostly hung out under the seats until it was time to stay in a hotel overnight. It's not so hard. Now, sometimes they howl and yowl. It depends also on what you can tolerate. My son and I exchanged a cat each. We changed vehicles so I was stuck driving the car, which had
his cat in it. He had my baby. They both calmed down once they were with their perspective 'people'. Just must constantly check on food and especially water. We DID learn small rodents (my poor daughter's robo dwarf hamsters) do
not travel. All but one (she had 4) died. But the cats were good. They're really pretty hardy, little guys. Feel free to ask me anything if you should want. And I'm sure the others here are knowledgeable as well. I wish you the best in your venture!
They're worth it!